The phase relationships in the ZrO₂-YO_1.5-TaO_2.5 (ZYTO) system at 1250 °C—a temperature of interest for thermal barrier coatings applications—were investigated using precursor-derived powders. The system is bisected by a quasi-binary joining the tetragonal (t) ZrO₂ and monoclinic (M’) YTaO₄ solid solutions. The mutual solubility limits for these phases differ significantly depending on whether the third phase in equilibrium with t and M’ is fluorite or the orthorhombic (O) Zr₆Ta₂O₁₇. More importantly, the tetragonal phase in equilibrium with fluorite is non-transformable to the monoclinic form upon cooling, whereas that in equilibrium with O, which has lower stabilizer content, is transformable. The behavior contrasts with that previously observed for the equilibrium at 1500 °C, wherein the t phase on both sides of the quasi-binary is non-transformable. The fluorite solid solution extends from the ZrO₂-YO_1.5 binary to the YO_1.5-TaO_2.5 binary at 1250 °C, as previously shown for 1500 °C.

使用前驱物衍生的粉末研究了ZrO ₂ -YO _1.5 -TaO _2.5（ZYTO）系统在1250°C（对于热障涂层应用而言非常重要的温度）中的相位关系。该系统通过将四角（t）ZrO ₂和单斜晶（M'）YTaO ₄固溶体连接起来的准二元对分。这些相的互溶极限取决于与t和M'平衡的第三相是萤石还是正交晶（O）Zr ₆ Ta ₂ O ₁₇。更重要的是，与萤石平衡的四方相在冷却后不可转变为单斜晶形式，而与O平衡的四方相则具有较低的稳定剂含量，因此可转变。该行为与先前在1500°C时观察到的平衡状态相反，在该温度下，准二进制的两面均为不可变形的t相。萤石固溶体在1250°C时从ZrO ₂ -YO _1.5二元延伸到YO _1.5 -TaO _2.5二元，如先前在1500°C所示。